Flashcards in Chapter 25 & 26 - The Urinary System and Excretion and Fluid Balance Deck (59)
Materials Excreted by the Urinary System
Any substance which is in excess in the body
Nitrogenous wastes, such as urea, creatinine, and uric acid.
Excretion and Homeostasis
Because even essential substances can be excreted if in too a quantity, excretion plays a major role in maintaining the proper concentrations for the body fluids. Consequently is a major contributor to homeostasis
Urinary System Anatomy
- The kidneys
- The ureters
- The urinary bladder
- The urethra
- Regulate the composition and volume of blood and body fluids
- Excrete waste from the blood
- Regulate erythropoiesis
- Aid in regulating pH
- Regulate blood pressure by releasing Renin which activates the angiotensin system
- Assists the liver in detoxification, deamination, and gluconeogenesis
External Anatomy of the Kidney
The kidneys resemble large beans which an indent called the hilus, which is where the ureter exits. There are 3 tissue layers which surround the kidney.
The innermost layer. A fibrous membrane that protects against trauma.
The middle layer. Protects against shock and helps hold the kidneys in place. A mass of fatty tissue, a cushiony layer.
A very thin connective tissue. It anchors the kidney to the body wall. It's very very thin and may become disconnected. It also surrounds the adrenal glands
Innermost layer. It consists of 5 to 14 renal pyramids. The loop of Henle is usually found here. The pyramids face outwards, and their apex, the renal papillae, are directed towards the center.
The outer layer. It dips down in between the pyramids forming the renal columns, where most of the nephrons are found.
Minor Calyx, Major Calyx, and Renal Pelvis
Each pyramid empties into a funnel shaped space, the minor calyx, which then becomes larger and forms the major calyces. They then form a larger space, the renal pelvis, which empties into the ureter.
The sire of urine formation and consequently represents the functional unit of the kidney.
A filter, the beginning of the kidney tube. Double walled and has specialized capillaries which form a ball called the glomerulus. The capillaries are fenestrated, making them very permeable. The outer layer is composed of squamous epithelium, the inner layer has special epithelial cells called podocytes, which have slits.
Proximal Convoluted Tubule
Highly twisted, lined with cells that have microvilli and mitochondria.
Loop of Henle
Where the tube straightens out, it forms a long hairpin shape. Two parts, the descending which is thinner, and the ascending which is thicker.
Distal Convoluted Tubule
The last of the renal tubule. It is highly twisted and surrounded by capillaries.
The distal convoluted tubule empties out here. May have many nephrons emptying out here. Not technically part of the nephron.
Types of Nephrons
(1) Cortical Nephrons = Glomeruli are found on the outer portion of the cortex. Lack a loop of Henle and usually don't even reach down into the medulla. About 85% of nephrons.
(2) Juxtamedullary Nephron - The glomerulus lies in the cortex close to the border of the medulla. It has a loop of Henle which penetrates deep into the medulla. Their major role is water balance.
Circulation in the Kidney
Renal artery ---> segmental arteries ---> lobar arteries ---> interlobar arteries ---> arcuate arteries ---> interlobular arteries ---> afferent arterioles ---> glomerulus ---> efferent arterioles ---> peritubular capillary beds.
The nerve supply of the kidney
Urine formation. Filtration occurs across glomerular walls; nutrient absorption occurs primarily in the proximal convoluted tubule; secretion occurs primarily in the distal convoluted tubule; the loop of Henle regulates water and Na+ loss.
Essentially the same process that occurs across every capillary wall, but much more efficient in the glomerulus.
Glomerular Capillary Membrane
Much more permeable than the average capillary. It has completely open pores and only a basement membrane. It has a very high surface area.
Glomerular Blood Pressure
Very high, about 60 mmHg. Because of this, the efferent arteriole is smaller in diameter than the afferent. The osmotic pressure is an opposing force which tries to pull the fluid back into the glomerulus, about 30 mmHg. Pressure between the layers is about 20 mmHg. Net is about 10 mmHg.
Glomerular Filtration Rate (GFR)
About 25% of the cardiac output flows through the kidney. Insulin is the standard at 125. If theres a clearance value lower than that, it means the substance is partially reabsorbed. If it's higher, it means the tubule cells must be secreting.
It's highly selective compared to filtration. Most solutes are reabsorbed by active transport, some co-transport, and some diffusion. Nutrients like glucose and AA are too important to be lost, so the goal is for 100% to be reabsorbed. which doesn't always happen.
The concentration in the plasma that must be exceeded before it appears in the urine. The tubular maximum which equates to the maximum amount of the substrate that the tubule can reabsorb, the rest is lost in urine.
Substances are actively secreted from the blood to the nephron tubule. Only a few can be secreted, H+, K, NH3, creatinine, and some drugs. This helps regulate pH.
This is the elimination of urine from the bladder.